1. Field of the Invention
The present invention relates to an oil pressure reduction rate restricting apparatus for a V-belt type continuously variable transmission, which is capable of restricting the rate of reduction in the target primary pressure and the target secondary pressure.
2. Description of the Prior Art
Conventionally, a V-belt type continuously variable transmission (hereinafter referred to as “belt CVT”) using a V belt has been known as a continuously variable transmission which can be suitably applied to a vehicle. The belt CVT is constructed by winding the V-belt around a primary pulley and a secondary pulley, and groove widths of the primary pulley and the secondary pulley are variably controlled by oil pressure.
A first cylinder chamber and a second cylinder chamber are provided to the primary pulley and the secondary pulley, respectively. Further, the belt CVT is comprised of an oil pressure calculating section that calculates a primary pressure which is supplied to the first cylinder chamber and a secondary pressure which is supplied to the second cylinder chamber. The groove widths of the primary pulley and the secondary pulley are changed according to the oil pressures supplied to the respective cylinder chambers, and the gear ratio continuously varies according to the radius of contact between the V belt and each of the pulleys (Japanese Laid-Open Patent Publication No. 5-240331, for example).
The conventional belt CVT as described above, however, has the problem that in the case where the oil pressure calculating section instructs a rapid decrease in the primary pressure or the secondary pressure (e.g., in the case where an accel pedal is suddenly released), the actual primary pressure or the actual secondary pressure undershoots the target oil pressure. This results in a shortage in torque capacity, which has an adversary effect on gear ratio shifting.